A mass flow controller is widely used in order to control the supply amount of process gas supplied into a chamber in a manufacturing process of a semiconductor. A mass flow controller is constituted by a mass flowmeter which monitors a mass flow rate of process gas, a flow control valve and a control circuit which control the mass flow rate, etc. Furthermore, the flow control valve is constituted by a passage through which the process gas flows, a valving element which opens the passage at a predetermined opening position or intercepts the same, and an actuator which drives the valving element.
In the technical field of a semiconductor, miniaturization and high integration have proceeded to a limit. For example, in the case of a microprocessor used for the newest personal computer, the width of a wiring circuit is made finer to about 20 nm, and a plurality of cores are mounted in one piece of microchip. In order to perform a film forming process and fabrication process of a semiconductor having such a precise and complicated structure with a high accuracy, various kinds of process gas which has not been used conventionally is used increasingly.
For instance, although there is a possibility that vaporization gas of a certain kind of liquid material and sublimation gas of a certain kind of solid material may condense in a piping at an ordinary temperature since their vapor pressure is very low, it has been attempted to introduce such a condensable gas into a semiconductor manufacturing equipment without condensation and to use it for a manufacturing process of a semiconductor, by heating and holding all the piping system leading to a chamber at an elevated temperature not less than a critical temperature (for instance, not less than 300° C.).
However, a heat-resistant temperature of a laminated piezoelectric actuator widely used as an actuator which drives a valving element of a flow control valve is generally 120° C., and it is 150° C. even in the case of an actuator for an elevated temperature. At a temperature higher than this heat-resistant temperature, an insulation breakdown of an internal electrode occurs within a short time, and it becomes impossible to drive a valving element.
Therefore, even when condensable gas at an elevated temperature is dealt with in a mass flow controller, some proposals for preventing the temperature of a laminated piezoelectric actuator from rising and holding it not higher than its heat-resistant temperature have been made. For instance, Japanese Patent Application Laid-Open “kokai” No. 2004-162733 discloses a configuration of a flow control valve comprising a spacer which is located between a laminated piezoelectric actuator and a valving element, transmits the operation of the laminated piezoelectric actuator to the valving element, and radiates heat transmitted from the valving element side. In this flow control valve, since most heat transmitted from the fluid to be controlled is emitted to open air from a cooling fin disposed on the outer periphery of the spacer, the rise in temperature of the laminated piezoelectric actuator is suppressed.
Moreover, for example, Japanese Patent Application Laid-Open “kokai” No. 2011-117499) discloses a configuration of a flow control valve comprising a spacer for lifting and supporting a laminated piezoelectric actuator so as to keep the laminated piezoelectric actuator away from a passage of fluid and for radiating heat transmitted from the fluid to the laminated piezoelectric actuator. In this flow control valve, the heat received from the fluid is radiated while being transmitted from the lower end portion to the top end portion of the spacer, and the length (height dimension) of the spacer is set to be longish so that the temperature of the part contacting the laminated piezoelectric actuator may become not more than the heat-resistant temperature of the laminated piezoelectric actuator.